<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        .box{
            display: flex;
            height: 100vh;
        }

        .box > div:nth-child(1){
            width: 200px;
            background: red;
        }

        .box > div:nth-child(2){
            flex: 1;
            background: yellow;
        }

        .box > div:nth-child(3){
            width: 300px;
            background: green;
        }
    </style>
</head>
<body>
<div class="box">
    <div>1</div>
    <div>1</div>
    <div>1</div>
</div>
</body>
</html>
